1. Field of the Invention
The present invention relates to immersion cleaning, and in particular to a method and apparatus for removing small particles from solid substrates.
2. Description of the Related Art
Unless extraordinary precautions are taken, virtually all workpieces and manufactured items acquire or retain particulate contaminants on their surfaces during manufacture. The presence of such fine particles can deleteriously affect product quality in a wide variety of applications (for example, fabrication of semiconductors and precision instruments such as inertial guidance instruments). Particles of micrometer size or smaller are generally observed to adhere tenaciously and non-specifically to other solid surfaces, and cannot be removed by simple mechanical means or with cleaning techniques developed primarily for degreasing purposes.
Traditional techniques of removing unwanted particles include the use of chlorinated cleaning agents such as chlorofluorocarbons and methylchloroform; these, however, have been found to constitute major sources of atmospheric chlorine, which is responsible for devastation of the ozone layer. Alternative approaches have stressed the use of non-chlorinated cleaning agents. See, e.g., U.S. Pat. No. 4,711,256 (to Kaiser, entitled METHOD AND APPARATUS FOR REMOVAL 0F SMALL PARTICLES FROM A SURFACE).
Thus far, however, particle-removal materials and techniques have been used in conjunction with non-specialized equipment such as vapor degreasers. These devices, while serviceable, do not control the cleaning process in a manner directly responsive to removal of particles. For example, a user may clean an article, remove it from the cleaning solution, microscopically examine it for the continued presence of contaminating particles, and repeat the process until the particle count reaches a small enough level. Not only is this iterative procedure time-consuming and inefficient, but can also result in evaporative loss of cleaning solvent during the unproductive examination steps. Alternatively, articles can be subjected to cleaning for such an extended period as to virtually ensure the absence of particles. Once again, this approach results in unnecessary cleaning effort.